Modern Japanese are still written that way. There are several apps/editors that support that writing mode because it's one of the requirements in the publishing industry in Japan.

More precisely, newspapers, most books (except technical/scientific ones) and magazines are written in the vertical form. Comics too. Business documents are typically all horizontal.

Also they have a uber-complex w3c standard (draft) to support this system: https://w3c.github.io/jlreq/#vertical_writing_mode_and_horiz...